Pyrolysis of tetrafluoroethylene polymer



Patented Feb. 12, 1946 2,394,531 KYROLYSIS F TETRAFLUOROETHYLENE POLYME Anthony F. Benning, Woodstown, and Frederick B. Downin Carneys Point, N. J., and Joseph D. Park, Wilmington, DeL, assignors to Kinetic Chemicals. Inc., Wilmington, Del.. a-corporation of Delaware No Drawing. Continuation of application Serial No. 484,314, April 23, 1943.

This application October 4, 1943, Serial No. 504,952

8 Claims.

A. This invention relates to fluorinated carbon compounds and to processes of producing them by pyrolysis. Pyrolysis means the transformation of a substance by a process in which heat alone is the effective agent. This is a continuation of U. 8. Serial No. 484,314, filed April 23, 1943.

B. It is an object of the invention to prepare new compounds. Another object of the invention is to prepare new and old compounds by a process which is technically and economically satisfactory and which is superior to known processes of producing those compounds which are old. Another obiect of the invention is to produce organic fluorine compounds and particularly to prepare perfluorinated hydrocarbons. Another object of the invention is to produce fluorinated compounds which previously had been made only by the use of elementaI fluorine. Another object of the invention is to prepare lubricants particularly useful for systems in which a high diflerentlal pressure exists on the opposite sides of a friction Joint. A particular object of the invention is to produce hexa-fiuoro-cyclo-propane, having the empirical formula CaFe, and the structure:

F! r,o- -----cFi C. The objects of the invention are accomplished, generally speaking, by the pyrolysis of polymerized tetrafluoro-ethylene.

D. The process is carried out in general by heating poly-tetra-fiuoro-ethylene in a closed system at a temperature high enough'to produce a pyrolytic reaction but below that at which decomposition of the reaction products occurs. In general, temperatures from about 450 C. to 700 C. have been found useful, with a very 'efiicient reaction occurringbetween 570 to 630 C. The polymer of tetra-fluoro-ethylene used in the following examples sintered at about 500 C. Different polymers of tetra-fiuoro-ethylene may have diflerent characteristics and the temperature will be selected to produce the optimum results in view 01' those characteristics.

E. The reaction is carried out in an apparatus whose materials are substantially inert to the reaction and the reaction products. carried out satisfactorily in the presence of an inert gas, such as nitrogen, and may also be carrier out in the presence of chlorine.

F. Elevated and reduced pressures may be used wherever they will produce increased efliciency of reaction. In general, the reactions proceed eili ciently at atmospheric pressure,

About 33 parts of' granular ttra-flucro-ethylene polymer were fed intermittently into a platihum-lined Inc'onel-iacketed nickel tube, 0.75" x {18" long at a rate of about 15 parts per hour. The

tube temperature was maintained at about 575 C. over a length of 12" by electrical heating. The

pyrolysis products were first passed through a trap for solids and the vapors condensed in a carbonice-acetone trap backed by a liquid nitrogen trap. vA lower melting solid polymer trapped in the first trap had a melting range of 70-300" C. The liquid condensates were washed with water,

.dried and condensed. The crude organic product (33 parts) had the following composition:

C4Fl::::::::::::: IIIIIIIIIIIIIII III Low melting polymers; melting range 70-300 0.

Example If One hundred and forty parts of tetra-fluoroethylene polymer were fed intermittently into an It may be Inconel tube 1" x 26" long, at a rate of about 40 parts per hour. A tube temperature of 580- 620" C. was maintained. (This temperature was measured with a thermocouple wrapped outside of the pyrolysis tube.) A steady flow of about 1-2 liters per hour of nitrogen was passed through the tube during the pyrolysis. The pyrolysis products were first passed through a 2-liter flask which acted as a trap for solids and then through a receiver cooled in carbonice-aceton and backed by a liquid nitrogen-cooled trap. About.130 parts of pyrolysis products were obtained. This represented an organic recovery of about 93%.

The liquid condensates were washed, dried and analyzed. The composition of the pyrolysis products were as follows:

Weigh:

n B g I on used) C1174 76 a. F0 -m cm. -5 33 Fraction IV 3 Low melting polymer 15 Loss 7 Example III Abount 436 parts of heat-treated tetra-fluoroethylene polymer (granular polymer was first molded in the cold and then subjected to about 2000 p. s. i. abs. at 320 C. for about half an hour) were pyrolyzed under conditions similar to that described in Example II.

The pyrolysis products obtained did not differ materially from the composition of the products obtained in Example II.

Example IV A similar pyrolysis was carried out in a steel tube 1" x 26" long, at a tube temperature of 620-630 C., at a rate of about parts 0! tetrafluoro-ethylene polymer per hour. Carbonize.- tion was evident and the pyrolysis products had the iollowing composition:

Weigh:

roen ig" (hand on P Y used) CsF 76 24 C] F. E. 5 C.F -5 l3. 5 CsFm 23 4. 4 40 C. and above 2. 2 Lower melting polymer. 7. 4 Organic recovery 80 Example V About 70 parts of tetra-fluoro-ethylene polymer and '70 parts of chlorine were fed per hour into an Inconel tube heated to 630 C. The pyrolysis products were first led through a trap for solids, then through receivers cooled in carbonice-acetone and in liquid nitrogen. The liquid condensates were then later washed (to remove excess chlorine), dried. and analyzed. A total of 79 parts of pyrolysis product was recovered. The

H. The process which has been hereinbeiore described and illustrated is a most efllcient method of producing carbon-ring compounds saturated with fiuorine. These compounds have the general formula CnF2n, a number of which have been made by methods of the prior art, but others of which are new. Particularly notable among the new compounds which are formed are CsFs and Cd's, otherwise known as hexa-fiuoro-cyclopropane and octo-fluoro-cyclo-butane, respectively. Cal"; is claimed in this application and Cd: is claimed in an application of Downing, Benning and McHamess, Serial No. 535,208, filed May 11, 1944. In addition to the compounds of this homologous'series, there have been produced certain polymeric substances having a melting range between 70-300 C., the precise structures of which, due in part to the difliculty in determining polymeric structures, have not been determined. All 0! these polymeric compounds are new and useful in the field of plastics and are claimed herein. These low-melting polymers have a putty-like consistency, are insoluble in the usual organic solvents such as C014, CHCla', petroleum ether, octane, benzene, methanol, concentrated caustic alkalis, inorganic acids and hot concentrated mineral acids. The low-melting polymers are homogeneous and possess good lubricating qualities. They have been used as lubricants ior friction Joints through which organic and inorganic liquids were passed at elevated temperatures and high vacuum, and, when so used, have maintained the seal without breaking. For example, glass and metal stop cocks and valves have been coated with the polymers and the seal so formed has proved highly eflective. They have also been used as a sealing material for a glass ball-and-socket joint between a distillation flask and a reflux column in a vacuum system in which the sealing compounds were exposed to organic substances heated to more than 200 C. under a pressure of less than 1 mm. This extreme pressure diflerential had no eilect upon the seal. These low-melting polymers are useful as protective coating for metal, glass and other surfaces and or the lubrication of moving parts, particularly where those parts are exposed to solvents or other active chemicals.

I. In the following table is a list 01! pure compounds which have been isolated from the pyrolysis of poly-tetra-fluoro-ethylene and identified.

Lower melting polymers were also found which had a melting range oi 70 to 300 C.

J. The compound, cm, was identified through its boiling point, molecular weight, and through the formation of the known dibromide CzFiBrz, boiling at 47.6 C.

K. CaFs was identified through its molecular weight (vapor density at 22 C. and 647 mun-5.4 g. per liter; MW. found: 153; calc.: and chlorination with elemental chlorine in the vapor phase in the presence of light to the known compound C1(CF:):C1, boiling at about 35 C. Fluorination of CaFu with SbFs yielded a small amount of the known compound Cal's. boiling at --36 C. The new compound, Cal's, did not decolorize a solution or bromine in CO1 although it decolorized permanganate solution. On thi basis a cyclic structure is assigned to this compound.

L. C41 was identified through its molecular weight (vapor density at 22 C. and '15! mm.

8.44 g. per liter; M.W. found: 204; calc. 200). This compound did not decolorize a solution of bromine when the mixture was exposed to sunlight in a gas pressure flask. SbFs was without effect on 04F: even after prolonged heating at 160 C. Thi ver stable compound ,is identical Fraction IV," which was itself separated into 7 three fractions which app l-red, by comparison of boiling point only, to have the constitutions: CsF1o2+23C; CcF12i+51-53 C.; C1F1u+80 C; residue about 90-130 C. decolorized bromine solution in carbon tetra: chloride and they appeared in general to correspond to similar compounds of like empirical formula which had previously been prepared by the action of elemental fluorine on carbon or benzene.

N. Most of the products of the reaction are possessed-of outstanding thermal and chemical stability and, because of their properties are'use ful for avariety of commercial purposes, such as solvents, reaction media, heat-transfer media and for power generation. Many of them are non-corrosive and generally non-toxic. They are,'c0nsequently, desirable for use as refrigerants and as intermediates for the making of completel fluorinated compounds. The new lowmelting polymers are quite inert to chemical reagents.

O. This process invention is aneasy and inexpensive method of producing perfiuorinated compounds which heretofore have been produced only with great difliculty and with poor yields through the use of elemental fluorine.

P. As many apparently widely diflerent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiment thereof except as defined in the appended ,ciaims.

- We claim:

1. The compound having the mula Cal's, a boiling point about -28 0., and a vapor density of 5.4 g. per liter at 647 mm. pressure and 22 C.

2. The process which comprises heating a polymer of tetraiiuoroethylene in the presence of chlorine at a temperature of about 630 C. and

separating the reaction products.

3.Theprocesswhichcomprisesheating polymerisedtetrafluoroethylenatoatemparatureof fromaboutbOO'Qtoabout'lWOJorape'riod None of those fractions empirical tor of time suflicient to cause pyrolysis of the polymerized tetraflucroethylene and separating the pyrolysis products.

4. The process which comprises heating polymerized tetrafiuoroethylene to a temperature of from about 500 C. to about 700 C. in an inert reaction chamber for a period of time sumcient to cause Pyrolysis of the polymerized tetrafluoroethylene and the formation of a substantial proportion of compounds of the formula Cd's, wherein n represents an integer of at least 2, and separating compounds of the formula CIF-si from the reaction mixture.

5. The process which comprises heating polymerized tetrafluoroethylene to a temperature of from about 500 C. to about 700 C. in an inert reaction chamber in the presence of an inert gas for a period of time sufficient to cause pyrolysis of the polymerized tetrafiuoroethylene and the formation of a substantial proportion of compounds of the formula CnF2n, wherein n represents an integer of at least 2, and separating compounds of the formula CnF'aa from the reaction mixture.

6. The process which comprises heating polymerized tetrafiuoroethylene to a temperature of from about 500 C. to about 700 C. in an inert reaction chamber for a period of time suflicient to cause pyrolysis of the polymerized tetrafluoroethylene and the formation of a substantial proportion of a compound of the formula CsFs and merised tetraiiuoroethylene to a temperature of from about 500 C. to about 700 C. in an inert reaction chamber for a period of time sufficient to cause pyrolysis of the polymerized tetrafluoroethylene and the formation of a substantial proportion of compounds boiling from about -76 C. to about 82 C. and having the formula Cal as. wherein n represents an integer of at least 2, and low melting polymers having a melting range between 10 C. and 300 C., and separating from the reaction mixture compounds of the formula fractions.

55 Bel a and the low melting polymers in separate arrrnomr r. BENNING. mmmrcx n. nownma. Joseph D. PARK. 

